Radio waves pick up explosives

New techology is being used to detect explosives, like those in landmines. So fields like this one in the Golan Heights region of Israel may be easier to clear (Image: Reuters/Yonathan Weitzman)

Scientists in Japan are using radio waves rather than x-rays to detect explosives such as TNT in landmines or luggage.

They say their new technique is better than conventional methods of detection and can identify different types of white powder, from flour and salt to drugs and explosives.

The technique can also identify landmines, an improvement from traditional metal detectors that cannot tell bits of metal in the ground from an actual mine.

“Until now it has been very difficult to detect specific explosives such as TNT because they contain atoms of nitrogen that vibrate at very low frequencies,” says Professor Hideo Itozaki at Osaka University, one of the authors of the paper published in the latest issue of the journal Superconductor Science and Technology.

He says the lower this resonant frequency, the harder it is to detect which atoms are present in a molecule. This, in turn, makes it harder to define what the molecule or substance is.

To overcome this, the scientists turned to a technique called nitrogen quadrupole resonance, which uses radio waves to detect atoms of nitrogen in different positions in a molecule.

For example, a nitrogen atom attached to a carbon atom will have a different resonance to one attached to an atom of oxygen.

Because the molecular structure of each explosive is different, the resonant frequency will be different.

The scientists then developed a device to detect these subtle differences in vibrations, a superconducting quantum interference device, or SQUID.

The device, which is only about 1 centimetre across, operates at -196°C, so needs liquid nitrogen to cool it.

“This will not hinder the equipment from being used in places such as airports as liquid nitrogen is becoming much easier to deal with and is already routinely used in hospitals and laboratories,” says Itozaki.

One hitch for now, though, is that the screening time takes “several minutes”, something the team is working to improve.